1. Field of the Invention
The present invention relates to an electronic device having a master control unit and a slave control unit.
2. Description of the Related Art
In a multifunctional copier (so-called digital multifunction peripheral) having multiple functions such as copy, printer and facsimile functions, electrical components such as motors and fans required to operate the device are distributed throughout the chassis. To control these components, typically a control system is constituted by a control board serving as master and multiple control boards serving as slaves for controlling parts of the copier in coordination with the master control board. Recently, with such master-slave distributed control systems, serial communication has been used as the communication method between the master control board and the slave control boards. Using serial communication enables the number of signals to be cut, allowing for cost reductions due to the cut in wiring. With a master-slave distributed control system, a technique for protecting the system if a problem arises with a slave control board is essential.
As a technique for protecting a master-slave distributed control system, Japanese Patent Laid-Open No. 2006-110150, for example, discloses a configuration in which a master control unit and a slave control unit are connected by a communication line, and a watchdog timer that monitors the operation of the CPU on the slave side is provided in the slave control unit. In this configuration, the master control unit issues an initialization command to the watchdog timer of the slave control unit at a prescribed interval (e.g., 100 ms) via the communication line, and loads an initial countdown value (e.g., 3 sec). A reset signal output from this watchdog timer is connected to a reset terminal of the CPU on the slave side, and the CPU on the slave side is reset when the countdown reaches zero without the initial value being loaded due to a system error or the like.
With Japanese Patent Laid-Open No. 2006-110150, a watchdog timer for monitoring and resetting a slave control unit needs to be provided in each slave control unit if there are multiple slave control units. The number of watchdog timers and related peripheral circuit components is thus increased with an increase in the number of slave control units, resulting in cost increases. An increase in the number of components also increases the sources of trouble.